The present inventive subject matter relates to stunning and/or euthanization of laboratory fish using electric currents and the monitoring of the laboratory fish to prevent injury thereof.
The effect of electric currents on fish are well known in the prior art and especially in the general techniques of electrofishing. Electrofishing involves the use of electric currents to attract and/or repel fish with the intent of creating aquatic barriers, sample fish barriers, and/or to increase collection yields.
It has been established that relatively small potentials that are impressed across the body of a fish invoke a flight reaction. Larger potentials result in the alignment of the fish with the electric current, or electrotaxis. Still larger potentials may result in unconciousness or complete euthanasia of the fish. (See Introduction to Electrofishing, pages 24-26, Smith-Root, Inc. which is incorporated herein by reference).
Electrofishing has traditionally been used in freshwater lakes and streams and is the subject of U.S. Pat. Nos. 5,445,111; 5,327,854; 4,750,451; 4,672,967; 4,713,315; 5,111,379; 5,233,782; 5,270,912; 5,305,711; 5,311,694; 5,327,668; 5,341,764; 5,551,377; and 6,978,734 which are incorporated herein by reference. Also, electrofishing has been the used to stimulate yields of fishing in conjunction with the use of trawl nets as described in U.S. Pat. Nos. 3,110,978 and 4,417,301 which are also incorporated herein by reference.
Systems for controlling electricity in aquatic environments have been described in U.S. Pat. No. 5,460,123 which is incorporated herein by reference.
There are also electrofishing systems that attempt to reduce the leaching of metal ions into water due to the electrolytic action of passing current through the solution. Also systems for monitoring small laboratory fish using cameras are described in U.S. Patent Publication 2006/0018833 which is incorporated herein by reference.
Therefore in the prior art, a considerable body of work is associated with the electrification of large bodies of water to impress electric fields across larger fish, such as salmon or trout, as compared to smaller fish, that would be typically be used for the purpose of laboratory experimentation.
The use of small fish, in particular zebrafish, are popular as biological models for scientific studies. The studies involve placing fish in laboratory desktop tanks, then subjecting the fish to physical, chemical, or biological stress. This is followed by an examination of the subject fish to determine the various effects on the fish as a result of the stresses. For the purpose of this application the term “fish” will refer to any suitable aquatic laboratory fish, including, but not limited to zebrafish.
A recurring problem with the examination of laboratory fish is that they tend to be very active. Also laboratory fish are dimensionally very small. The small size of the fish combined with their activity can impair the researcher from making precise scientific measurements unless the fish is caught and inspected.
Therefore there is a need for the laboratory researcher to euthanize laboratory fish in a relatively quick and painless manner. Ideally the state of euthanasia can be controlled for a period of time in which the measurement of the fish is needed. To induce euthanasia an electric field is applied to the water in the tank. This, in turn, induces an electric field across the body of the fish. This amount of electricity that is passed through the fish varies based on the orientation of the fish and the magnitude of the electric field.
Low electric fields evoke a deterrent response in the fish causing the fish to be repelled from the electric field. Greater electric fields may evoke an involuntary response that results in the fish being attracted and swimming towards the anode and away from the cathode. Still larger electric fields may result in a state of narcosis being induced in the fish. Higher electric fields may result in euthanasia (i.e. death) of the fish.
Prior art solutions and techniques that induce euthanasia in fish involve the addition of chemicals to the tank. Chemicals used for euthanasia are expensive to acquire, pose a storage and maintenance problem, and are at risk of degradation. These chemicals, which are toxic to fish, may have the unfortunate consequence of skewing laboratory results during any post-euthanasia pathology. Furthermore, the researcher runs the risk of exposure to the chemicals that are used to euthanize the fish. Also, the use of chemicals to euthanize fish may be unnecessarily complex and expensive, which would result in the added cost of training specialized personnel.
Furthermore, there is also a view that the chemical euthanasia of fish may induce unnecessary pain. In response, the American Veterinary Medical Association (AVMA) Panel on Euthanasia has listed three acceptable methods of euthanasia for fish, and two conditionally acceptable methods. These methods include the use as acceptable of such chemicals as tricaine methanesulfonate (MS-222), benzocaine (related to MS-222 but less soluble in water) and barbituates.
In view of the high cost and risk of certain chemical agents that induce euthanasia in fish, there is a need to have a unit that will induce unconsciousness and euthanasia in laboratory fish without chemicals. There is also a need for a portable unit that can euthanize fish without the use of chemical agents. There is also a need for a unit that will shield the researcher from contact with potentially hazardous chemical agents. There is also a need for unit that can euthanize fish using electrical currents. There is also a need for a unit that can euthanize fish using rechargeable batteries.
There is also a need to have a monitoring system to insure that a laboratory fish does not come into contact with an anode or a cathode to reduce the risk of injurious shock to the fish.
There is also a need to reduce the leaching of anions into the solution (e.g. fish water) during fish euthanasia. In certain cases, a laboratory fish may be euthanized first by transferring to a euthanasia tank, then followed by actual euthanasia, then disposal. During operation, anions will leach from the electrodes via electrolytic action resulting in the further contamination of the water. It is therefore desirable to have a unit that minimizes the leaching of anions from an electrode during euthanasia.
Therefore, what is desired is an apparatus to immobilize fish and place the fish in the state of euthanasia. It is also desired that this apparatus operate at relatively low voltage levels. It is also desired is an apparatus that is portable. It is also desired that the apparatus prevent the leaching of anions from electrodes into the water electrodes during operation.